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Optics Letters

Spontaneous breaking of time translation symmetry in a system without periodic external driving

Timofey T. Sergeev, A. A. Zyablovsky, E. S. Andrianov, Yu. E. Lozovik

Published Jul 31, 2024• 2 citations
Publisher

Abstract

It is known that spontaneous time translation symmetry-breaking can occur in systems periodically driven at a certain period. We predict a spontaneous breaking of time translation symmetry in an atom-cavity system without external driving, in which a time scale is determined by the time of light bypass of the resonator. We demonstrate that there is a parameter range, in which a system state returns to its initial state only after two bypasses of the resonator. We believe that the predicted phenomenon opens a way to a new direction in the time crystal field.

DOI
10.1364/ol.527514

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It is known that spontaneous time translation symmetry-breaking can occur in systems periodically driven at a certain period. We predict a spontaneous breaking of time translation symmetry in an atom-cavity system without external driving, in which a time scale is determined by the time of light bypass of the resonator. We demonstrate that there is a parameter range, in which a system state returns to its initial state only after two bypasses of the resonator. We believe that the predicted phenomenon opens a way to a new direction in the time crystal field.
It is known that the spontaneous time translation symmetry breaking can occur in systems periodically driven at a certain period. We predict a spontaneous breaking of time translation symmetry in an atom-cavity system without external driving, in which a time scale is determined by the time of light bypass of the resonator. We demonstrate that there is a parameter range, in which a system state returns to its initial state only after two bypasses of the resonator. We believe that the predicted phenomenon opens a way to a new direction in the time crystal field.
Time crystals are classified as discrete or continuous depending on whether they spontaneously break discrete or continuous time translation symmetry. Although discrete time crystals have been extensively studied in periodically driven systems, the experimental realization of a continuous time crystal is still pending. We report the observation of a limit cycle phase in a continuously pumped dissipative atom-cavity system that is characterized by emergent oscillations in the intracavity photon number. The phase of the oscillation was found to be random for different realizations, and hence, this dynamical many-body state breaks continuous time translation symmetry spontaneously. Furthermore, the observed limit cycles are robust against temporal perturbations and therefore demonstrate the realization of a continuous time crystal.
Time crystals are many-body states that spontaneously break translation symmetry in time the way that ordinary crystals do in space. While experimental observations have confirmed the existence of discrete or continuous time crystals, these realizations have relied on the utilization of periodic forces or effective modulation through cavity feedback. The original proposal for time crystals is that they would represent self-sustained motions without any external periodicity, but realizing such purely self-generated behavior has not yet been achieved. Here, we provide theoretical and experimental evidence that many-body interactions can give rise to an inherent time crystalline phase. Following a calculation that shows an ensemble of pumped four-level atoms can spontaneously break continuous time translation symmetry, we observe periodic motions in an erbium-doped solid. The inherent time crystal produced by our experiment is self-protected by many-body interactions and has a measured coherence time beyond that of individual erbium ions.
Time crystals are physical systems whose time translation symmetry is spontaneously broken. Although the spontaneous breaking of continuous time-translation symmetry in static systems is proved impossible for the equilibrium state, the discrete time-translation symmetry in periodically driven (Floquet) systems is allowed to be spontaneously broken, resulting in the so-called Floquet or discrete time crystals. While most works so far searching for time crystals focus on the symmetry breaking process and the possible stabilising mechanisms, the many-body physics from the interplay of symmetry-broken states, which we call the condensed matter physics in time crystals, is not fully explored yet. This review aims to summarise the very preliminary results in this new research field with an analogous structure of condensed matter theory in solids. The whole theory is built on a hidden symmetry in time crystals, i.e., the phase space lattice symmetry, which allows us to develop the band theory, topology and strongly correlated models in phase space lattice. In the end, we outline the possible topics and directions for the future research.
Spontaneous symmetry breaking is a ubiquitous concept and is well described in many textbooks of physics. However, direct observation of spontaneous symmetry breaking is lacking. Here we present the observation and analysis of a spontaneously broken discrete time-translation symmetry in our driven system. We experimentally find a 50-50 split between two stable and temporal-distinct solutions, indicative of the breaking of a Z2{\mathbb{Z}}_{2}Z2​ (Ising-like) time-translation symmetry. The experiment allows for further exploration of the symmetry breaking in our discrete time crystal and for engineering excitations in space and time in the quantum domain.
Spontaneous symmetry breaking plays a pivotal role in physics ranging from the emergence of elementary particles to the phase transitions of matter. The spontaneous breaking of continuous time translation symmetry leads to a novel state of matter named continuous time crystal (CTC). It exhibits periodic oscillation without the need for periodic driving, and the relative phases for repetitively realized oscillations are random. However, the mechanism behind the spontaneous symmetry breaking in CTCs, particularly the random phases, remains elusive. Here we propose and experimentally realize two types of CTCs based on distinct mechanisms: manifold topology and near-chaotic motion. We observe both types of CTCs in thermal atomic ensembles by artificially synthesizing spin-spin nonlinear interactions through a measurement-feedback scheme. Our work provides general recipes for the realization of CTCs, and paves the way for exploring CTCs in various systems.